Carbosilane Precursors For Low Temperature Film Deposition

ABSTRACT

Provided are processes for the low temperature deposition of silicon-containing films using carbosilane precursors containing a carbon atom bridging at least two silicon atoms. Certain methods comprise providing a substrate; in a PECVD process, exposing the substrate surface to a carbosilane precursor containing at least one carbon atom bridging at least two silicon atoms; exposing the carbosilane precursor to a low-powered energy sourcedirect plasma to provide a carbosilane at the substrate surface; and densifying the carbosilanestripping away at least some of the hydrogen atoms to provide a film comprising SiC. The SiC film may be exposed to the carbosilane surface to a nitrogen source to provide a film comprising SiCN.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. Non-Provisional applicationSer. No. 13/609,867, filed Sep. 11, 2012, which claims priority to U.S.Provisional Application No. 61/534,122, filed Sep. 13, 2011, and is acontinuation-in-part of U.S. Non-Provisional application Ser. No.13/288,157, filed Nov. 3, 2011, the contents of both of which are herebyincorporated by reference in their entirety.

TECHNICAL FIELD

Embodiments of the present invention generally relate to the field offilm deposition, and specifically to precursors for low temperaturedeposition of films containing silicon, carbon and nitrogen.

BACKGROUND

In the manufacture of electronic devices such as integrated circuits, atarget substrate, such as a semiconductor wafer, is subjected to variousprocesses, such as film formation, etching, oxidation, diffusion,reformation, annealing, and natural oxide film removal.Silicon-containing films are an important part of many of theseprocesses.

Silicon-containing films are used for a wide variety of applications inthe semiconductor industry. Examples of silicon-containing films includeepitaxial silicon, polycrystalline silicon (poly-Si), and amorphoussilicon, epitaxial silicon germanium (SiGe), silicon germanium carbide(SiGeC), silicon carbide (SiC), silicon nitride (SiN), siliconcarbonitride (SiCN), and silicon carboxide (SiCO). As circuit geometriesshrink to smaller feature sizes, lower deposition temperatures forSi-containing films are preferred, for example, to reduce thermalbudgets.

Silicon nitride films have very good oxidation resistance and insulatingqualities. Accordingly, these films have been used in many applications,including oxide/nitride/oxide stacks, etch stops, oxygen diffusionbarriers, and gate insulation layers, among others. Several methods areknown for forming a silicon nitride film on the surface of asemiconductor wafer by Chemical Vapor Deposition (CVD). In thermal CVD,a silane gas, such as monosilane (SiH₄) or polysilanes, is used as asilicon source gas.

SiN film formation has also been carried out via atomic layer depositionusing halosilane and ammonia. However, this process requires hightemperatures, in excess of 500° C., to effect clean conversion andeliminate NH₄X byproducts. In device manufacturing, processes that canbe performed at lower temperatures are generally desired for thermalbudget and other reasons.

SUMMARY

One aspect of the invention relates to a method of forming a layer on asubstrate surface. The method comprises: providing a substrate; in aPECVD process, exposing the substrate surface to a carbosilane precursorcontaining at least one carbon atom bridging at least two silicon atoms;exposing the carbosilane precursor to a low-powered energy source (e.g.,direct plasma) to provide a carbosilane at the substrate surface; andstripping away at least some of the hydrogen atoms to provide a filmcomprising SiC.

Another aspect of the invention relates to a method of forming a layeron a substrate surface, the method comprising: providing a substrate; ina PECVD process exposing the substrate surface to a carbosilaneprecursor containing at least one methylene bridging two silicon atoms;exposing the carbosilane precursor to a direct plasma to provide acarbosilane at the substrate surface; stripping away at least some ofthe hydrogen atoms; and exposing the carbosilane surface to a nitrogensource to provide a film comprising SiCN suitable as a low k dielectricfilm.

Various embodiments are listed below. It will be understood that theembodiments listed below may be combined not only as listed below, butin other suitable combinations in accordance with the scope of theinvention.

In one or more embodiments of either aspect, stripping away at leastsome of the hydrogen atoms comprises exposing the substrate surface to aplasma containing one or more of He, Ar and H₂. In some embodiments ofeither aspect, the film comprising SiC has a ratio of Si:C approximatelymatching that of the carbosilane precursor.

In some embodiments of either aspect, the carbosilane precursor is oneor more of 1,3,5-trisilapentane, 1,3-disilabutane, 1,3-disilacyclobutaneand 1,3,5-trisilacyclohexane. In further embodiments, the carbosilaneprecursor comprises 1,3,5-trisilapentane. In even further embodiments,the SiC film has a ratio of Si:C of about 3:2. In an alternativeembodiment, the carbosilane precursor comprises 1,3-disilabutane.

The process conditions may be varied. In one or more embodiments ofeither aspect, exposing the carbosilane precursor to a low-poweredplasma results in polymerization of the carbosilane. In some embodimentsof either aspect, the low-powered plasma has an RF value of about 50 Wto about 500 W. In some embodiments, the low-powered plasma has a valueof about 10 W to about 200 W. In one or more embodiments of eitheraspect, the carbosilane precursor is exposed to the low-powered plasmafor between 0.10 seconds and 5.0 seconds. In some embodiments of eitheraspect, the substrate surface has a temperature of about 100 and about400° C.

In one or more embodiments of either aspect, exposing the carbosilane toa nitrogen source comprises exposing the carbosiliane to a plasmacontaining nitrogen. In some embodiments, exposing the carbosiliane to aplasma containing nitrogen results in the formation of N—H bonds thatpromote irreversible attachment of a monolayer of the carbosilane to thesubstrate surface. In some embodiments, exposing the carbosilane to anitrogen source comprises flowing ammonia or nitrogen gas.

In some embodiment, the SiC or SiCN film is suitable as a low kdielectric film.

A third aspect of the invention relates to a method of forming a layeron a substrate surface, the method comprising: providing a substrate;exposing the substrate surface to a carbosilane precursor1,3,5-trisilapentane, 1,3-disilabutane, 1,3-disilacyclobutane and1,3,5-trisilacyclohexane; exposing the carbosilane precursor to alow-powered plasma to provide a carbosilane at the substrate surface;and exposing the carbosilane to a plasma comprising H₂. Any of the aboveembodiments may also be used with this aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-C are Fourier transform infrared spectra of three SiCN filmsformed in accordance with an embodiment of the invention;

FIG. 2 is a Fourier transform infrared spectra of a SiCN film formed inaccordance with an embodiment of the invention;

FIG. 3 is a Fourier transform infrared spectra of a SiCN film formed inaccordance with an embodiment of the invention; and

FIG. 4 is a Fourier transform infrared spectra of a SiCN film formed inaccordance with an embodiment of the invention.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the invention, it isto be understood that the invention is not limited to the details ofconstruction or process steps set forth in the following description.The invention is capable of other embodiments and of being practiced orbeing carried out in various ways.

A “substrate surface” as used herein, refers to any substrate ormaterial surface formed on a substrate upon which film processing isperformed during a fabrication process. For example, a substrate surfaceon which processing can be performed include materials such as silicon,silicon oxide, strained silicon, silicon on insulator (SOI), carbondoped silicon oxides, silicon nitride, doped silicon, germanium, galliumarsenide, glass, sapphire, and any other materials such as metals, metalnitrides, metal alloys, and other conductive materials, depending on theapplication. Substrates include, without limitation, glass sheets,ceramic substrates and semiconductor wafers. Substrates may be exposedto a pretreatment process to polish, etch, reduce, oxidize, hydroxylate,anneal and/or bake the substrate surface. In addition to film processingdirectly on the surface of the substrate itself, in the presentinvention any of the film processing steps disclosed may also beperformed on an underlayer formed on the substrate as disclosed in moredetail below, and the term “substrate surface” is intended to includesuch underlayer as the context indicates.

As used herein, an “SiH-containing precursor” refers to a precursormolecule that contains a plurality of Si—H bonds. SiH-containingprecursors include silanes and carbosilanes. The term “silanes” refersto compounds which contain silicon and hydrogen atoms, includingsilicon-to-hydrogen bonds. The term “carbosilanes,” which may be usedinterchangeably with “organosilanes,” refers to compounds that containsilicon, hydrogen and carbon atoms, and contain at least onecarbon-to-silicon covalent bond. Thus, a “halogenated Si—H-richprecursor” or “halogenated silane” or “halogenated carbosilane” refersto a precursor molecule where at least one of the hydrogen atoms bondedto a silicon atom is replaced with a halogen. By extension, a “cyanatedSi—H-rich precursor” or “cyanated silane” or “cyanated carbosilane”refers to a precursor molecule where at least one of the hydrogen atomsbonded to a silicon atom is replaced with a cyano (CN) group.

As used herein, “containing at least one carbon atom bridging at leasttwo silicon atoms” refers to a carbosilane that contains an Si—C—Sicomponent. The carbon may have two hydrogens, which would constitute amethylene group and result in a Si—CH₂—Si component. The silicon atomsmay have a wide variety of substituents, including, but not limited to,hydrogen or additional silicon and/or carbon atoms. In some cases, thecarbon atom may bridge three or four silicon atoms.

As used herein, “low temperature” refers to processes that are conductedat less than 400° C. In specific embodiments, low temperature refers toless than 300° C., and in more specific embodiments, less than 200° C.and in highly specific embodiments, less than 100° C.

As used herein, “low-powered energy source” refers to a source of energythat will not damage carbosilane precursor deposited at a substratesurface. For example, where the source of energy is a plasma, the RFvalue is less than about 200 W.

One aspect of the invention relates to a method of forming a layer on asubstrate surface, the method comprising providing a substrate, exposingthe substrate surface to a carbosilane precursor containing at least onecarbon atom bridging at least two silicon atoms, exposing thecarbosilane precursor to a low-powered energy source to provide acarbosilane at the substrate surface, densifying the carbosilane, andexposing the carbosilane surface to a nitrogen source. The process thenmay be repeated to add additional layers.

Described herein are PECVD processes to deposit SiC and SiCN films.Accordingly, one aspect of the invention relates to a method of forminga layer on a substrate surface, the method comprising: providing asubstrate; in a PECVD process, exposing the substrate surface to acarbosilane precursor containing at least one carbon atom bridging atleast two silicon atoms; exposing the carbosilane precursor to a lowpowered energy source to provide a carbosilane at the substrate surface;and stripping away at least some of the hydrogen atoms to provide a filmcomprising SiC. In one or more embodiments, the low powered energysource comprises a direct plasma.

In specific embodiments, carbosilane precursors containing at least onecarbon atom bridging at least two silicon atoms are used to produce thinfilms of SiC. In some embodiments, these thin films of SiC can then beconverted to SiCN by displacing some of the carbon atoms from the SiC.Carbosilane precursors, as described herein, are used to deposit a thinlayer of a silicon-containing film. While not wishing to be bound by anyparticular theory, it is thought that the carbosilane is polymerized atthe substrate surface after exposure to a low-powered energy source. Thecarbosilane precursor is exposed to a low-powered energy source, whichforms a layer of the precursor on the substrate surface. In oneembodiment, exposing the carbosilane precursor to a low-powered energysource comprises exposing the carbosilane precursor to an electron beam.In another embodiment, exposing the carbosilane precursor to alow-powered energy source comprises exposing the carbosilane precursorto a low-powered plasma. In a specific embodiment, the low-poweredplasma has a value of about 10 W to about 200 W or about 50 W to about500 W. In some embodiments, the RF value of the plasma ranges from about10, 20, 30, 40, 50, 60 70, 80 or 90 W to about 175, 200, 225, 250, 275or 300 W. In another embodiment, the precursor is exposed to thelow-powered plasma for between about 0.10 seconds and about 5.0 seconds.

Carbosilane precursors have been demonstrated to undergo efficientdensification/dehydrogenation to silicon-rich SiC. Thus, according tovarious embodiment, carbosilane precursor at the substrate surface is atleast partially densified/dehydrogenated. In one embodiment,densification/dehydrogenation is plasma-induced. A helium, argon and/orhydrogen-containing plasma may be used for dehydrogenation. In specificembodiments, dehydrogenation involves the use of plasma containing H₂.

In addition to densification/dehydrogenation, nitrogen may be introducedinto the SiC layer by nitridation to form SiCN. This occurs by exposingthe carbosilane surface to nitrogen source. In one embodiment, thiscomprises flowing ammonia or nitrogen gas. In an alternative embodiment,nitridation occurs via exposure to a nitriding plasma. In a morespecific embodiment, this nitriding plasma comprises N₂. In a furtherembodiment, around 5% of the plasma comprises N₂. In yet anotheralternative embodiment, nitridation does not occur.

These deposition processes can be accomplished using relatively low RFpower conditions and at temperatures lower than previously available. Inprevious methods, higher temperatures of more than 500° C. werenecessary. In specific embodiments, substrate temperature duringdeposition can be lower than about 400, 350, 300, 250, 200, 150 or 100°C.

Precursors are based on carbosilanes. Carbosilanes, sometimes alsoreferred to as organosilanes, are compounds containing carbon-to-siliconcovalent bonds. According to certain embodiments, the carbosilaneprecursors should be chosen such that there is reduced fragmenting indeposited films. Fragmentation of the film to volatile fragmentsprevents densification, and causes shrinking and cracking in flowableapplications.

Carbosilanes may be linear, branched or cyclic. A particularly suitabletype of carbosilane is one that contains a bridging methylene groupsbetween at least two silicon atoms, such that the carbon in themethylene group is bonded to the at least two silicon atoms. In afurther embodiment, the methylene group bridges two silicon atoms.Either one, both, or neither of the two silicon atoms may be halogenatedor pseudohalogenated. Higher carbosilanes with an extended Si—C—Sibackbone are particularly suitable as they tend towards dehydrogenativedensification reactions, instead of fragmentation. In anotherembodiment, the carbosilane contains a bridging CH₂ group or simple Catom between three or four silicon atoms respectively. Precursorswithout such bridging methylene groups, such as those initiallycontaining only terminal methyl substituents may undergo rearrangementson plasma excitation to form methylene bridged carbosilanes and are thusalso suitable, though in this case there may also be substantialcleavage of the Si—C bond of the Si—CH₃ substituent.

Polycarbosilanes containing more extended backbones of alternatingSi—C—Si—C—Si bonds, such as 1,3,5-trisilapentane, are particularlypreferable. Examples of suitable carbosilane precursors include, but arenot limited to 1,3,5-trisilapentane, 1,3,5-trisilacyclohexane,1,3-disilabutane, 1,3-disilapropane and 1,3-disilacyclobutane. In aparticular embodiment, the carbosilane precursor is 1,3-disilabutane. Inanother particular embodiment, the carbosilane precursor is1,3,5-trisilapentane. Where a desired level of carbon is desired and theprecursor contains only terminal methyl substituents, it is generallynecessary to begin with precursors possessing at least twice the Si:Cratio desired in the final film.

In some cases, the conformality of films deposited using such low powerplasma steps may be sufficiently conformal such that even aftersubsequent densification they may provide “ALD-like” conformality. Auseful way to enhance such conformality is to employ a plasma activationstep at the end of the activation sequence—such as one resulting in theformation of N—H bonds—that promotes the irreversible attachment of thefirst monolayer of precursor deposited in a low power plasma step, whilesubsequently deposited materials are bound reversibly, and may re-enterthe gas phase and be purged away during a subsequent purge step.Accordingly, in one embodiment, exposing the carbosilane to a plasmacontaining nitrogen results in the formation of N—H bonds that promoteirreversible attachment of a monolayer of the carbosilane to thesubstrate surface. While the final surface activation, appliedimmediately prior to the introduction of precursor but after a plasmadensification, may be a step involving nitrogen plasma, it may alsoinvolve a non plasma step such as simple exposure of the surface to aflow of ammonia (NH₃).

Generally, exposure of “seed” films containing Si, C, and H to Ncontaining plasmas is effective for generating films exhibiting N—Hfunctionality as detectable by growth of a characteristic absorptionbetween about 3200-3600 cm⁻¹ in the FTIR. Typical conditions entailpressures in the range of 0.5 Torr to 20 Torr and RF power levels (13.56MHz, direct plasma) of between 25 W and 500 W, for example 100 W for aduration of 2 sec at a total pressure of 4 Torr and partial pressure ofnitrogen between about 1 Ton and 3 Torr, the balance being He or Ar. Incases where the film being treated contains very little H (for exampleif a plasma process has already been performed to remove H) a smallamount of hydrogen may also be added to the plasma mixture to promotethe generation of more N—H bonding.

The ratio of silicon to carbon in the film may be adjusted, depending onthe plasma power, exposure time and temperature. For example, the ratioof Si:C can readily be reduced in a SiCN composition by replacing carbonwith nitrogen atoms using post-treatment plasmas. The ratio of C to Simay be increased by utilizing precursors containing a higher initialratio. In one or more embodiments, the ratio of Si:C is approximatelythe same as that of the precursor. Thus, for example, in one or moreembodiments, if 1,3,5-trisilapentane is used as the precursor, the Si:Cratio of the film may be about 3:2. Generally, carbosilane precursorscontaining carbon in a bridging position between two silicon atoms canbe consolidated to carbide-type ceramics with efficient retention ofcarbon. On the other hand, carbon is not retained to such extent wherethe precursor does not contain a bridging carbon atom. For example,precursors based on methylsilanes undergo consolidation with substantialloss of carbon.

Another aspect of the invention relates to exposure of the substratesurface to plasma as part of the process of forming the film or layer.The surface with bound precursor is exposed to adensification/dehydrogenation plasma. Suitable dehydrogenation plasmasinclude, but are not limited to, H₂, He and Ar. The surface is thenexposed to a nitriding plasma. Suitable nitriding plasmas include, butare not limited to N₂ and ammonia. Exposure to the plasmas may be donesubstantially simultaneously or sequentially. Substantially simultaneousmeans that the substrate surface is exposed to both plasmas at the sametime, with little exposure time to one plasma at a time. When donesequentially, the dehydrogenating plasma may first be applied, followedby the nitriding plasma. Any number of sequences may be used. In oneembodiment, plasma exposure may occur in every step of the process. Inanother embodiment, plasma exposure may occur every other sequence.Subsequent exposure to a nitriding plasma results in conversion of theSiC film to SiCN.

In one embodiment of this aspect, dehydrogenation and nitridation occursubstantially simultaneously. By contrast, in another embodiment,dehydrogenation and nitridation occur sequentially.

Accordingly, in a second aspect of the invention, the invention relatesto a method of forming a layer on a substrate surface, the methodcomprising providing a substrate, exposing the substrate surface to acarbosilane precursor containing at least one methylene bridging twosilicon atoms, exposing the carbosilane precursor to a low-poweredplasma to provide a carbosilane at the substrate surface, densifying thecarbosilane, and exposing the carbosilane surface to a nitrogen source.Such a SiCN may be suitable for use as a low k dielectric film. In oneembodiment of this aspect, the low-powered plasma has a value of about10 W to about 200 W. In a different embodiment of this aspect, thecarbosilane precursor is exposed to the low-powered plasma for between0.10 seconds and 5.0 seconds.

In a different embodiment, the carbosilane precursor is one or more of1,3,5-trisilapentane, 1,3-disilabutane, 1,3-disilacyclobutane and1,3,5-trisilacyclohexane. In a more specific variant of this embodiment,the carbosilane precursor is 1,3,5-trisilapentane.

A third aspect of the invention relates to a method of forming a layeron a substrate surface, the method comprising: providing a substrate;exposing the substrate surface to a carbosilane precursor1,3,5-trisilapentane, 1,3-disilabutane, 1,3-disilacyclobutane and1,3,5-trisilacyclohexane; exposing the carbosilane precursor to alow-powered plasma to provide a carbosilane at the substrate surface;and exposing the carbosilane to a plasma comprising H₂

In some embodiments, one or more layers may be formed during a plasmaenhanced chemical vapor deposition (PECVD) process. In some processes,the use of plasma provides sufficient energy to promote a species intothe excited state where surface reactions become favorable and likely.Introducing the plasma into the process can be continuous or pulsed. Insome embodiments, sequential pulses of precursors (or reactive gases)and plasma are used to process a layer. In some embodiments, thereagents may be ionized either locally (i.e., within the processingarea) or remotely (i.e., outside the processing area). In someembodiments, remote ionization can occur upstream of the depositionchamber such that ions or other energetic or light emitting species arenot in direct contact with the depositing film. In some PECVD processes,the plasma is generated external from the processing chamber, such as bya remote plasma generator system. The plasma may be generated via anysuitable plasma generation process or technique known to those skilledin the art. For example, plasma may be generated by one or more of amicrowave (MW) frequency generator or a radio frequency (RF) generator.The frequency of the plasma may be tuned depending on the specificreactive species being used. Suitable frequencies include, but are notlimited to, 2 MHz, 13.56 MHz, 40 MHz, 60 MHz and 100 MHz. Althoughplasmas may be used during the deposition processes disclosed herein, itshould be noted that plasmas may not required. Indeed, other embodimentsrelate to deposition processes under very mild conditions without aplasma.

According to one or more embodiments, the substrate is subjected toprocessing prior to and/or after forming the layer. This processing canbe performed in the same chamber or in one or more separate processingchambers. In some embodiments, the substrate is moved from the firstchamber to a separate, second chamber for further processing. Thesubstrate can be moved directly from the first chamber to the separateprocessing chamber, or it can be moved from the first chamber to one ormore transfer chambers, and then moved to the desired separateprocessing chamber. Accordingly, the processing apparatus may comprisemultiple chambers in communication with a transfer station. An apparatusof this sort may be referred to as a “cluster tool” or “clusteredsystem”, and the like.

Generally, a cluster tool is a modular system comprising multiplechambers which perform various functions including substratecenter-finding and orientation, degassing, annealing, deposition and/oretching. According to one or more embodiments, a cluster tool includesat least a first chamber and a central transfer chamber. The centraltransfer chamber may house a robot that can shuttle substrates betweenand among processing chambers and load lock chambers. The transferchamber is typically maintained at a vacuum condition and provides anintermediate stage for shuttling substrates from one chamber to anotherand/or to a load lock chamber positioned at a front end of the clustertool. Two well-known cluster tools which may be adapted for the presentinvention are the Centura® and the Endura®, both available from AppliedMaterials, Inc., of Santa Clara, Calif. The details of one suchstaged-vacuum substrate processing apparatus is disclosed in U.S. Pat.No. 5,186,718, entitled “Staged-Vacuum Wafer Processing Apparatus andMethod,” Tepman et al., issued on Feb. 16, 1993. However, the exactarrangement and combination of chambers may be altered for purposes ofperforming specific steps of a process as described herein. Otherprocessing chambers which may be used include, but are not limited to,cyclical layer deposition (CLD), atomic layer deposition (ALD), chemicalvapor deposition (CVD), physical vapor deposition (PVD), etch,pre-clean, chemical clean, thermal treatment such as RTP, plasmanitridation, degas, orientation, hydroxylation and other substrateprocesses. By carrying out processes in a chamber on a cluster tool,surface contamination of the substrate with atmospheric impurities canbe avoided without oxidation prior to depositing a subsequent film.

According to one or more embodiments, the substrate is continuouslyunder vacuum or “load lock” conditions, and is not exposed to ambientair when being moved from one chamber to the next. The transfer chambersare thus under vacuum and are “pumped down” under vacuum pressure. Inertgases may be present in the processing chambers or the transferchambers. In some embodiments, an inert gas is used as a purge gas toremove some or all of the reactants after forming the silicon layer onthe surface of the substrate. According to one or more embodiments, apurge gas is injected at the exit of the deposition chamber to preventreactants from moving from the deposition chamber to the transferchamber and/or additional processing chamber. Thus, the flow of inertgas forms a curtain at the exit of the chamber.

The substrate can be processed in single substrate deposition chambers,where a single substrate is loaded, processed and unloaded beforeanother substrate is processed. The substrate can also be processed in acontinuous manner, like a conveyer system, in which multiple substrateare individually loaded into a first part of the chamber, move throughthe chamber and are unloaded from a second part of the chamber. Theshape of the chamber and associated conveyer system can form a straightpath or curved path. Additionally, the processing chamber may be acarousel in which multiple substrates are moved about a central axis andare exposed to deposition, etch, annealing, cleaning, etc. processesthroughout the carousel path.

During processing, the substrate can be heated or cooled. Such heatingor cooling can be accomplished by any suitable means including, but notlimited to, changing the temperature of the substrate support andflowing heated or cooled gases to the substrate surface. In someembodiments, the substrate support includes a heater/cooler which can becontrolled to change the substrate temperature conductively. In one ormore embodiments, the gases (either reactive gases or inert gases) beingemployed are heated or cooled to locally change the substratetemperature. In some embodiments, a heater/cooler is positioned withinthe chamber adjacent the substrate surface to convectively change thesubstrate temperature.

The substrate can also be stationary or rotated during processing. Arotating substrate can be rotated continuously or in discreet steps. Forexample, a substrate may be rotated throughout the entire process, orthe substrate can be rotated by a small amount between exposure todifferent reactive or purge gases. Rotating the substrate duringprocessing (either continuously or in steps) may help produce a moreuniform deposition or etch by minimizing the effect of, for example,local variability in gas flow geometries.

The approaches of low temperature atomic layer deposition of SiCN andSiC films described above may also be used for the deposition ofextremely thin, defect-free and conformal films for applications outsideof the electronics industry. Such applications include for thepreparation of barrier and passivation layers. Additionally, the lowtemperature reactivity would make the processes applicable to thecoating of organic substrates, including plant- and animal-derivedtissues and materials. In some embodiments, the films described hereinare used in low k dielectric barrier applications. In one or moreembodiments, the deposited films are highly etch resistant and have arefractive index (RI's) of between about 1.7 and 2.2.

EXAMPLES Example 1

Three SiCN films were deposited using 1,3,5-trisilapentane using theconditions listed in the Table 1. Films 1, 2, and 3 were formed usingmultistep PECVD deposition and treatment-type sequences, with very lowpowers (20 W) and short times (0.25 sec) used in the first step. Thisvery low power and short exposure time formed 3-4 A of a “seed” layerper cycle. Upon completion of this first step, the flow of the1,3,5-trisilapentane precursor was turned off. A flow of inert gases wascontinued until residual traces of the precursor were purged from theprocess chamber. Once purge was completed, gas flows were readjusted andstabilized at the values selected for the first plasma treatment stepand again for a second plasma treatment step as indicated in Table 1.After completion of the full sequence, the entire cycle was thenrepeated until a desired film thickness was reached, for which themeasurements reported here was at least 100 A and more generally 200 Athick.

Films 1, 2, and 3 differed in respect to the plasma densification andnitrogenation steps employed. Film 2 was deposited in the same manner asFilm 1, but also featured exposure to a He/Ar plasma. Film 3 wasdeposited in the same manner as Film 2, but featured a nitrogen plasmaat 100 W, instead of the 200 W used for Films 1 and 2. Table 1 alsoshows the elemental composition of all three films deposited at thevarious conditions determined using Rutherford backscattering. It shouldbe noted that in this particular case analysis of the films for hydrogencontent was not performed, though there was likely residual hydrogenremaining behind in the films. Most relevant for comparisons to data onfilms derived from the precursor HMDS described in Example 2 are C:Siand N:Si ratios which can be calculated independent of the H content.Because 1,3,5-trisilapentane contains no nitrogen, all of the nitrogenincorporated into films derived from 1,3,5-trisilapentane can beattributed to the presence of nitrogen gas added during the plasmatreatments. The selection of specific treatment conditions provides somemeans for adjusting the final film composition.

TABLE 1 Elemental Content of Deposited Films BULK Films Film 2 Film 3Film 1: Deposition: Deposition: Deposition: 0.25 sec/20 Watt dep .25sec/20 Watt dep, 0.25 sec/20 Watt dep Treatments: Treatments Treatments:1.5 sec H₂ plasma at 100 W 1.5 sec H₂ plasma at 100 W 1.5 sec H₂ plasmaat 100 W, 2.5 sec He/Ar at 150 W 2.5 s He/Ar Plasma at 150 W Element2.10 sec N₂ Plasma at 200 W 3.5 sec N₂ Plasma at 200 W 3.2 sec N₂ Plasmaat 100 W Si 29 33 33 C 11 12 19 N 56 55 47 O 4 0 0 Ar 0.3 0.3 1Approximate (average) thickness of film removed by 5 min exposure todilute HF and etch raters based on 5 min etch time 30 Ang total 20 Angtotal No significant etch 6 Ang/min 4 Ang/min <1 Ang/min

Etch behavior was determined to be non-linear and, while not wishing tobe bound to any particular theory, appears to involve the relativelyrapid removal of a thin oxidized surface layer, after which subsequentextended exposure to the etchant has little effect. However, forconsistency in comparing results to those of Example 2, rates arereported based on a 5 min etch time in 100:1 HF. Similar behavior wasobserved using 6:1 BOE (6 parts concentrated NH₄F/1 part concentratedHF).

FIGS. 1A-C are graphical representations of Fourier transform infrared(FTIR) spectra of the SiCN films of Example 1. Film 1, which is atypical baseline process condition, is represented in FIG. 1C. Film 2 isrepresented in FIG. 1B. Film 3 is represented in FIG. 1A. Each of thethree datasets was normalized. The peak at about 3300 cm⁻¹ correspondsto N—H bonding. The peak at about 2300 cm⁻¹ corresponds to CO₂ presentin ambient air. The broad peak centered at around 900 cm⁻¹ correspondsto SiCN and the shift seen from Film 1. The shift seen from films 1 toFilm 3 is attributable to increasing carbon content, which alsocorresponds to their increasing resistance to wet HF etch chemistries.

Example 2

Additional SiCN films 4 through 6 were deposited using the precursorhexamethyldisilazane (HMDS) which has the formula [(CH₃)₃Si]₂NH.Accordingly, HMDS does not contain a carbon atom bridging at least twosilicon atoms. HMDS has a 3:1 carbon to silicon ratio, with each siliconatom bound to three methyl substituents and one nitrogen. A series ofcyclic depositions analogous used in depositing Films 1 through 3 wereemployed for the deposition of Films 4, 5, and 6, with results listed inTable 2 below. In each case, a “seed” layer was deposited at 20 W RF, 6Torr, delivering HMDS from a pressure controlled vapor draw ampouleusing Ar carrier gas analogous to conditions employed for1,3,5-trisilapentane in Example 1. The deposition rate was determined tobe approximately linear with total plasma on time/cycle and the initialstep followed by a long inert gas purge to remove residual precursorfrom the chamber. Film 4 was deposited using only a hydrogen plasmatreatment cycle. Film 5 was deposited with an H₂ plasma followed by a N₂plasma. Film 6 was deposited using plasma comprising a mixture of H₂ andN₂.

Table 2 also shows the elemental content of Films 4 through 6, asdetermined by Rutherford backscattering, as well as 100:1 wet HF etchrates. It should be noted that unlike in Films 1 through 3, Rutherfordbackscattering analysis for Films 4 through 6 included a determinationof hydrogen content in the films. Accordingly, direct comparisonsbetween Films 1 through 3 and Films 4 through 6 are limited to ratios ofcarbon to silicon or nitrogen to silicon.

TABLE 2 Elemental Content of Deposited Films Treatment Film 5 Film 41.10 sec H₂ Plasma at 300 W Film 6 Element 10 sec H₂ Plasma at 300 W 2.2sec N₂ Plasma at 100 W 7 sec H₂ + N₂ Plasma at 200 W Si 25.50% 26.50%32.50% C   34%   19%    0% N 18.50% 38.50% 47.50% O    0%    3%    9% H  22%   13%   11% 100:1 <1 Ang/min >20 Ang./min (complete loss >20Ang./min. (complete loss DHF or >100 A thick film in 5 min. of >100 Athick film in 5 min. Etch Rate

FIGS. 2-4 are graphical representations of Fourier transform infrared(FTIR) spectra of the Films 4 through 6, respectively. The results inFIG. 2 represent deposition followed by the use of an using an H₂ plasmaonly. The results in FIG. 3 represent deposition using an H₂ plasmafollowed by an N₂ (in sequence) plasma treatment analogous to thatapplied in Examples 1. The results in FIG. 4 represent deposition usinga plasma comprising a mixture of H₂ and N₂, and result in completeremoval of carbon from the film.

In contrast to the work with 1,3,5-trisilapentane, the conditionsnecessary to reduce C—H absorptions in the IR spectra and induce growthin the SiCN region at about 800-1000 cm⁻¹, were found to result insubstantial removal of carbon. In fact, without any additional treatmentthe C:Si ratio, as determined by RBS, dropped from the initial value of3:1 to only 1.3:1 While Film 4 was removed slowly in 100:1 HF, theapplication of additional steps involving a short N₂ plasma step (asseen in Film 5 and analogous to those employed in Example 1 films), oran alternative process which combined H₂ and N₂ plasmas into a singlestep (as seen in Film 6), underwent significantly higher carbon loss andexhibited low resistance to etching by 100:1 HF.

Interestingly, the N₂ plasma step added to each cycle of the processused for Film 4 process to give Film 5 resulted in the C:Si ratiodecreasing from 1.3:1 to 0.72:1, with the result still being higher thanthe ratios between 0.38:1 and 0.58:1 measured for the1,3,5-trisilapentane-derived Films 1-3. Yet it was the1,3,5-trisilapentane-derived films which exhibited superior etchresistance.

While not wishing to be bound by any particular theory, these resultssuggest the bridging carbon atoms present in precursors (and low powerseed films derived therefrom) are more effectively retained andconverted to etch resistant carbides than carbon originally present inthe form of terminal methyl groups. Furthermore, it should be noted thathigher RF power levels and longer H₂ and/or inert gas plasma treatmenttimes were necessary to promote condensation of HMDS derived seeds to alevel approximating the properties of a 1,3,5-trisilapentane-derivedfilms. All the films of Example 1 were prepared using a final Nitrogenplasma step (required for their conversion to SiCN—after which they wereshown to still exhibit reasonably high (and useful) resistance to wet HFetch processes. However, applying a similar process in the preparationof Film 5 (derived from the precursor HMDS) resulted in its loss of HFetch resistance—even though the final C:Si ratio remained higher (0.75)than measured in any of the 1,3,5-trisilapentane derived films. It maybe concluded that carbon originally present as “bridging” methylenesbetween Si atoms converts to a form exerting a much greater impact onetch behavior than can be estimated using compositional analysis alone.In the case of the 1,3,5 trisilapenetane, the addition of a nitrogenplasma step can effectively incorporate nitrogen without exerting alarge effect on the C:Si ratio (dropping from the value of 0.67:1calculated from the ratio in the precursor to 0.53:1 in the case of Film3). Adding an analogous Nitrogen plasma step at the end of thedensification process used for the HMDS Film 4 resulted in a much moresignificant impact on carbon content (1.3 dropping to 0.72 together witha severe degradation of etch resistance) suggesting the bonding of theretained carbon in each case is significantly different.

While it may indeed be possible to achieve a process with more classic,self-limiting reactivity by incorporating an active leaving group ontothe HMDS molecule (by replacing one of the methyl substituents with ahalide or cyanide), the stability of such a precursor may be severelycompromised by the potentially reactive, albeit somewhat hindered, N—Hbond already present. For this reason precursors possessing bothbridging carbon and reactive Si—H bonds (such as 1,3,5-trisilapentane)are particularly well suited as SiCN precursors, since carbon isefficiently retained while still permitting the introduction of Nitrogen(for example by inserting into Si—H bonds or Si—Si bonds). This resultsin the creation of reactive functionality not initially present in theprecursor itself, thereby enabling use of schemes employing the various“activated” derivatives described herein, most or all of which would notbe expected to be viable with an N—H functionality already present inthe molecule, as would be the case with a material derived from HMDS.

Therefore, the films of Example 2 show that compositions exhibitingdesirable etch properties required much longer and more aggressiveH₂/inert plasma based densifications steps, after which films were stillinsufficiently stable to permit use of a nitrogen plasma activation stepwithout significant loss of carbon and etch resistance. Thisdemonstrates the superiority of Example 1 films, deposited according tovarious embodiments of the invention.

Thus, there is an apparent advantage of precursors such as1,3,5-trisilapentane (which incorporate carbon in bridging positionsbetween Si atoms) relative to more common precursors possessingnon-bridging carbon substituents such as methyl (—CH₃), which isparticularly evident when targeting applications requiring that thefilms exhibit high wet etch resistance to chemistries such as HF (100:1H₂O/concentrated HF), or mixtures such as buffered oxide etch (a mixtureon 6:1 concentrated NH4F to concentrated HF) designed to rapidly etchSiO₂.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe invention. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the invention.Furthermore, the particular features, structures, materials, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Although the invention herein has been described with reference tospecific embodiments, it is to be understood that these embodiments aremerely illustrative of the principles and applications of the presentinvention. It will be apparent to those skilled in the art that variousmodifications and variations can be made to the method and apparatus ofthe present invention without departing from the spirit and scope of theinvention. Thus, it is intended that the present invention includemodifications and variations that are within the scope of the appendedclaims and their equivalents.

What is claimed is:
 1. A method of forming a layer on a substratesurface, the method comprising: providing a substrate; in a PECVDprocess, exposing the substrate surface to a carbosilane precursorcontaining at least one carbon atom bridging at least two silicon atoms;exposing the carbosilane precursor to a low-powered energy source toprovide a carbosilane at the substrate surface; and stripping away atleast some of the hydrogen atoms to provide a film comprising SiC. 2.The method of claim 1, wherein stripping away at least some of thehydrogen atoms comprises exposing the substrate surface to a plasmacontaining one or more of He, Ar and H₂.
 3. The method of claim 1,wherein the film comprising SiC has a ratio of Si:C approximatelymatching that of the carbosilane precursor.
 4. The method of claim 3,wherein the carbosilane precursor is one or more of1,3,5-trisilapentane, 1,3-disilapropane, 1,3-disilabutane,1,3-disilacyclobutane and 1,3,5-trisilacyclohexane.
 5. The method ofclaim 4, wherein the carbosilane precursor comprises1,3,5-trisilapentane.
 6. The method of claim 4, wherein the carbosilaneprecursor comprises 1,3-disilapropane.
 7. The method of claim 5, whereinthe SiC film has a ratio of Si:C of about 3:2.
 8. The method of claim 4,wherein the carbosilane precursor comprises 1,3-disilabutane.
 9. Themethod of claim 1, wherein exposing the carbosilane precursor to adirect plasma results in polymerization of the carbosilane.
 10. Themethod of claim 1 wherein the low-powered plasma has an RF value ofabout 50 W to about 500 W.
 11. The method of claim 1, wherein thesubstrate surface has a temperature of about 100 and about 400° C. 12.The method of claim 1, wherein the SiC film is suitable as a low kdielectric film.
 13. A method of forming a layer on a substrate surface,the method comprising: providing a substrate; exposing the substratesurface to a carbosilane precursor 1,3-disilapropane,1,3,5-trisilapentane, 1,3-disilabutane, 1,3-disilacyclobutane and1,3,5-trisilacyclohexane; exposing the carbosilane precursor to alow-powered plasma to provide a carbosilane at the substrate surface;exposing the carbosilane to a plasma comprising H₂.